Innovative Electromagnetic Coil Concepts for Multi-Equilibria Stellarator Design: Thickness variation, Electric dipoles, and Electric Current Sources/Sinks

Stellarators offer a promising path toward steady-state fusion power, but their reliance on complex coil systems—each designed to generate a single equilibrium—limits flexibility and scalability. This work introduces a set of novel coil concepts that enable the generation of multiple stellarator equilibria using a single winding surface, significantly reducing coil complexity and enhancing device adaptability. Four distinct methods are proposed and analyzed. The first method utilizes a single continuous conductor with spatially varying thickness, designed to replicate theoretical sheet currents derived from current potential functions. By solving for the conductivity distribution that satisfies Ohm's law, this approach enables high-accuracy reproduction of both quasi-axisymmetric and quasi-helically symmetric equilibria under realistic engineering constraints, including current density and electric field limits. The second method employs the superposition of electric dipoles on the winding surface. Here, localized voltage differences are used to drive incompressible, divergence-free surface currents. This approach allows non-invasive control of magnetic fields without requiring continuous current paths and offers fast reconfigurability through modulation of dipole strengths. A third method involves the use of discrete sources and sinks of current distributed across the winding surface. These injection and extraction points are optimized to reproduce desired magnetic fields. Finally, a multi-equilibria optimization framework is presented to generate multiple stellarator equilibria—such as quasi-axisymmetric and quasi-helically symmetric configurations—with a single winding surface. These methods enable a single device to access multiple magnetic field configurations and expand the design space for stellarator coils, offering new pathways toward compact, flexible, and experimentally agile fusion devices capable of accessing a wide range of plasma configurations.